The objective of the proposed research is to study the ocular motor subsystems in congenital nystagmus in a systematic manner to elucidate the pathophysiology of this disorder. Carefully controlled stimuli will be presented to patients to elicit responses from the smooth pursuit, saccadic, optokinetic and vestibulo-ocular subsystems, and eye movements will be recorded using techniques of electro-oculography. Analysis with computer techniques will be used to study quantitatively defects and interactions between these subsystems. Measurements will be made of 1) nystagmus waveforms, 2) effects of visual stimuli, gaze position and convergence on nystagmus, 3) smooth pursuit tracking, 4) saccadic tracking, 5) optokinetic responses to stimulation of the full visual field, 6) vestibulo-ocular responses to rotation and 7) effect of spontaneous head oscillations on nystagmus. Our investigations should lead to construction of a useful classification of the several, disparate forms of congenital nystagmus based on identification of specific defects in the ocular motor control system, which should improve our ability to diagnose these disorders. Understanding of the pathophysiology of congenital nystagmus eventually should result in improvements in the optical, pharmacologic and surgical treatment of this disorder.